Process for equilibrating allene and methylacetylene and for recovery of pure allene from the equilibrium mixture

ABSTRACT

METHYLACETYLENE AND ALLENE ARE EQUILIBRATED BY CONTACT WITH POTASSIUM HYDROXIDE IN AN INERT SOLVENT SUCH AS TBUTANOL. WHEN MIXTURES OF METHYLACETYLENE AND ALLENE ARE USED IN A CHEMICAL REACTION SUCH AS THE PREPARATION OF ISOPROPENYL STEARATE FROM STEARIC ACID AND ZINC STARATE IS THE SOLE CATALYST, METHYLACETYLENE IS SELECTIVELY ABSORBED BY THE STEARIC ACID LEAVING BEHIND HIGHLY PURIFIED ALLENE. ALTERNATIVELY, WHEN POTASSIUM STERATE IS PRESENT WITH THE ZINC STEARATE AND SUFFICIENT STEARIC ACID IS PRESENT, THE ALLENE-METHYLACETYLENE MIXTURE IS COMPLETELY ABSORBED. THE ZINC STEARATE-POTASSIUM STEARATE CO-FUNCTION SYNERGISTICALLY.

United States Patent 3,745,195 PROCESS FOR EQUILIBRATING ALLENE ANDMETHYLACETYLENE AND FOR RECOVERY OF PURE ALLENE FROM THE EQUILIBRIUMMIXTURE Edward S. Rothman, North Hills, and Samuel Serota, Philadelphia,Pa., assignors to the United States of America as represented by theSecretary of Agriculture N0 Drawing. Filed Aug. 31, 1971, Ser. No.176,735

Int. Cl. C07c 7/02 U.S. Cl. 260-6815 3 Claims ABSTRACT OF THE DISCLOSUREMethylacetylene and allene are equilibrated by contact with potassiumhydroxide in an inert solvent such as tbutanol. When mixtures ofmethylacetylene and allene are used in a chemical reaction such as thepreparation of isopropenyl stearate from stearic acid and zinc stearateis the sole catalyst, methylacetylene is selectively absorbed by thestearic acid leaving behind highly purified allene. Alternatively, whenpotassium stearate is present with the zinc stearate and sufficientstearic acid is present, the allene-methylacetylene mixture iscompletely absorbed. The zinc stearate-potassium stearate co-functionsynergistically.

A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sub-licenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

Processes for the equilibration of allene-methylacetylene mixturestypically involving a gas-phase, thermally facilitated operation using acatalyst of alumina or silica activated by a variety of halogens orhalogenated hydrocarbons are well known in the art (U.S. Patents 3,268,614, 2,594,706 and 3,243,470 and French Patents 1,370,- 415 and1,370,416). With one exception, US. Patent 3,268,614, none of theseclosely similar procedures attempt the difficult separation of pureallene from such mixtures. The difficulties of separation arise not onlybecause the boiling points of allene and methylacetylene are very closebut also because they distill together in an azeotropic constant boilingmixture. The exception referred to above involves selective complexformation with copper halide and is too costly for commercialapplication.

In previous studies concerning the addition of stearic acid tomethylacetylene to form the enol stearate, isopropenyl stearate(copending appl. Ser. No. 822,693, filed May 7, 1969), we were hamperedby the problem that cheap, commercially available welding-torch gasescontaining mixtures of allene and methylacetylene in about equalproportions were useful only for the methylacetylene content. Therecycling of the allene was expensive since equilibration by knownprocedures gave only a fixed proportion of methylacetylene requiring aninfinite geometric series for complete utilization.

An object of the present invention is to show that the known type ofequilibration can be achieved much more simply than previously possibleby using as catalyst potassium hydroxide in t-butanol or similar inertsemi-solvent.

In general, according to this invention we have found that when bothcomponents of the equilibrium are used in a given chemical reaction suchas the formation of isopropenyl stearate from stearic acid, it ispossible to isomerize simultaneously the allene to methylacetylene andabsorb this newly formed methylacetylene as rapidly as it is formed withstearic acid to form isopropenyl stearate. The continuously shiftingequilibration occurs until, provided suflicient stearic acid is present,all of the alice lene-methylacetylene mixture is consumed. In order toachleve complete consumption of the allene-methacetylene mixture thecatalyst must be a mixture of zinc stearate and potassium stearate. Theunusual and unpredictable synergism between these two stearates is animportant facet of this invention because there is a total lack ofreaction between stearic acid and allene when either catalyst is usedalone. Furthermore, we have found that the selectivity of stearic acidof methylacetylene to the exclusion of allene is so marked that allenemay be freed of any amount of methylacetylene provided that adequatestearlc acid is present and that the catalyst be only zinc stearate.

So far, for the sake of simplicity, we have specified stearic acid.However acids from acetic to n-cosanoic acid are suitable regardless ofwhether unsaturation is present or whether the acids are in a mixturesuch as those obtained from hydrolysed tallow or vegetable oils. Thezinc stearate and potassium stearate can be conventiently prepared insitu by adding to an excess of melted stearic acid the calculated amountof zinc oxide and/ or potassium hydroxide or similar basic salts capableof forming the required salts by neutralization.

We stated previously that the catalyst, potassium hydroxide, is in aninert solvent such as t-butanol. It is not strictly necessary that thesolvent dissolve all the potassium hydroxide or even that the solvent bepresent at all, but only that the solvent be inert. Solvents such asn-octadecanol and similar ones of lower molecular weight absorb bothallene and/or methylacetylene to form novel unsymmetrical isopropenylalkyl mixed ethers such as isopropenyl octadecyl ether M.P. 29.5-30" C.Ethers such as diethyl ether, dioxane, and tetrahydrofuran are suitablesemi-solvents for the indicated isomerization.

The indicated reactions are typically carried out in pressure vessels atC. and 600 p.s.i. pressure at the indicated temperature for 4 to 20hours reaction time. Occasionally, even much shorter times sufl'ice. Theexamples that follow will show the deviations allowable from theseconditions of time, temperature, and pressure without seriouslyaffecting the yield.

The utility of methylacetylene has been documented for enol estersynthesis. Allene essentially free of methylacetylene is useful as astarting material in the preparation of propargyl alcohol anticorrosiveformulations and for polymer synthesis, for example, methyl methacrylateproduction and polymerized allene per se.

EXAMPLE 1 t-Butanol, 250 ml. and 27 g. of freshly powdered commercialreagent potassium hydroxide were heated with slightly more than a moleof pure allene in an autoclave pressurized to 350 p.s.i. with nitrogenat room temperature and heated to 150 C. for 14 hours. The maximumdeveloped pressure was 560 p.s.i. Infrared assay of the gases showed thetypical equilibrium proportion of majority component methylacetylene andminority component allene.

EXAMPLE 2 Stearic acid, 282 g. (1 mole), and 30 g. of zinc stearate weremelted in an autoclave to a single phase and the vessel was sealed andwell purged with nitrogen. Propyne (methylacetylene) 16 g. (0.4 mole)and allene 16 g. (0.4 mole) were introduced via a pressure burette withnitrogen backup pressure, the vessel was heated to 150 C., andpressurized to 600 p.s.i. with additional nitrogen. After 14 hours, thecondensable head gases were verified by infrared analysis to be pureallene with only a trace of propyne. (Allene shows strong bands at 5.15and 5.9 microns in the gas infrared cell-regions of transparency forpropyne; propyne bands at 4.7 microns were practically absenta region ofallene transparency thus enabling an accurate assay.)

EXAMPLE 3 A pressure vessel was charged with 105 g. of stearic acid and7 g. of potassium hydroxide with stirring until solution occurred. Thevessel was then purged with nitrogen and sealed. 0.75 mole of liquidpure allene was added via a pressure burette having a back nitrogenpressure of 340 p.s.i. The vessel was heated to 150 C., for 12 hours andthen cooled. Examination of the vessel contents showed only the presenceof the starting materials allene and stearic acid and catalyst;methylacetylene and ester were absent.

EXAMPLE 4 A pressure vessel was charged with stearic acid, 282 g. (1mole), potassium hydroxide, 27 g. (0.5 mole approx.), and zinc stearate,42 g. Heat was generated during the neutralization causing vigorousexpulsion of steam. The vessel was sealed and flushed with nitrogen andthen 0.24 mole of allene and 0.24 mole of methylacetylene were added at150 C. using a back pressure of 600 p.s.i. to force the hydrocarbonsinto the vessel. After 17 hours, analysis of the head gas showed onlytraces of hydrocarbon in the head space indicating total conversion toisopropenyl stearate. Isolation of isopropenyl stearate, 160 g.,confirmed the analysis.

EXAMPLE 5 n-Octadecanol, 26 8 g. (1 mole), powdered potassium hydroxide,2.7 g. (.05 mole) and 1 mole of allene were heated to 150 C. for 24hours to yield the new compound n-octadecyl isopropenyl mixed ether. Theallene was totally consumed. The product was isolated by extraction withhexane-water mixture. The hexane was dried and very rapidly filteredthrough a short magnesium silicate column. Crystallization gave theproduct, M.P. 29.5-30 C.,

3125, 1627, 1588, 1458/1469 doublet, 1379, 1366, 1282, 1085, 794, 716cmf EXAMPLE 6 Results identical to those of Example 5 were obtainedusing a mole of propyne instead of a mole of allene.

We claim:

1. A process for the preparation of pure allene comprising reacting amember of the group consisting of saturated and unsaturated straightchain carboxylic acids having from 2 to 20 carbon atoms and mixtures ofsaid carboxylic acids with a mixture of methylacetylene and allene inthe presence of a zinc carboxylate salt.

2. The process of claim 1 wherein the member of the group is stearicacid and the zinc carboxylate salt is zinc stearate.

3. The process of claim 2 wherein the reaction is conducted at about C.under about 600 p.s.i. pressure for about 14 hours.

References Cited UNITED STATES PATENTS 2,953,611 9/1960 Spengler 260'6773,062,907 11/1962 Macht et al. 260681.5 C 3,268,614- 8/1966 Long260-6815 C DELBERT E. GANTZ, Primary Examiner V. OKEEFE, AssistantExaminer US. Cl. X.R.

